Tehran University of Medical Sciences Frontiers in Biomedical Technologies 2345-5837 0 0 2024 09 08 1019 1019 Asraa Sabah Abtan Pediatric and Preventive Dentistry Department, College of Dentistry, University of Baghdad, Baghdad, Iraq https://orcid.org/0009-0006-7520-1212 *Corresponding author: asraasabah90@gmail.com Nibal Mohammad Hoobi Pediatric and Preventive Dentistry Department, College of Dentistry, University of Baghdad, Baghdad, Iraq 2024 05 28 2024 07 24 Purpose: The present study aimed to evaluate the effectiveness of incorporating of nanohydroxyapatite in to hydrogen peroxide bleaching material on color, microhardness and morphological features of dental enamel. Materials and Methods: 33 sound maxillary first premolar were used for the study. Enamel blocks (7mm× 5mm×3mm) were prepared from the middle third of buccal halves of each tooth. Each dental block was embedded in self-curing acrylic resin with exterior enamel surface exposed for various applications. The dental blocks were  randomly divided into three groups (n=11) according to the bleaching technique. The groups were designed as follows: control; hydrogen peroxide (HP) and hydrogen peroxide with nanohydroxyapatite (HP-nHAp) groups. Color measurements and microhardness tests were conducted before and after treatment. one sample represented each group was selected for morphological analysis. Results: The  results showed  that both HP and HP-nHAp groups induced color changing. Enamel microhardness loss of HP group was significantly higher than that of HP-nHAp and control groups. The enamel morphological changes was only observed in HP group. Conclusion: nHAp could significantly reduce the enamel microharness loss caused by HP while preserving enamel surface morphological features without affecting bleaching efficacy. https://fbt.tums.ac.ir/index.php/fbt/article/view/1019 https://fbt.tums.ac.ir/index.php/fbt/article/download/1019/439